1. Technical Field
The present invention relates to a medical imaging modality for evaluating and quantifying necrotic cardiac tissue, and more particularly, to a system and method for tracking and classifying left ventricular tissue as viable or non-viable using cine-delayed enhancement magnetic resonance (Cine-DEMR).
2. Discussion of the Related Art
In the aftermath of a heart attack, the identification and assessment of non-viable (necrotic) tissue is necessary for effective development of intervention strategies and treatment plans for certain types of heart disease. For example, those tissues which are healthy or capable of recovery through coronary bypass, stent placement, etc., should be distinguished from those which are non-viable, or irreversibly damaged. In this manner, predictions may be made as to which patients might benefit from revascularization to increase their cardiac function and survival rate.
Physicians currently rely on several non-invasive indicators for determining viability of myocardial tissue. For example, the morphology of the myocardium, specifically its thinning, is evidence of necrotic tissue. In addition, abnormal motion, such as passive movement of a region or in extreme cases no movement at all can indicate myocardial damage. However, although morphology and functional changes are indicative of tissue abnormality, they are not sufficiently sensitive to differentiate abnormal from non-viable tissue.
Contrast enhanced imaging techniques may also be used to help identify non-viable regions. For example, positron-emission tomography (PET) and single-photon-emission tomography SPECT are capable of indicating viability information through differential signal intensity. However, these modalities are of limited utility as their resolution is quite low and are not generally available in the case of PET.
Another contrast enhanced imaging technique, DEMR, has been shown to enable direct visualization of non-viable myocardium. DEMR is an imaging technique in which non-viable myocardial tissue appears with increased signal intensity. DEMR is typically performed using a standard inversion recovery MR acquisition sequence 20-30 minutes after administration of a paramagnetic contrast agent (e.g., gadopentetate dimeglumine (Gd-DTPA)). DEMR has been shown to have sufficient spatial resolution to accurately distinguish viable (normal or ischemic) from non-viable myocardium within the left ventricular wall.
Radiologists typically acquire DEMR images in conjunction with other functional modalities (e.g., Cine MR), and use domain knowledge and experience to isolate the non-viable tissues. One recently developed technique stemming from the acquisition of DEMR images in conjunction with Cine MR is Cine-DEMR. Cine-DEMR is targeted to the left ventricle (LV) and combines the advantages of both Cine MR and DEMR. Similar to Cine MR, Cine-DEMR displays the heart beating over time allowing for the detection of motion abnormalities used to determine cardiac health. Similar to DEMR, in Cine-DEMR, non-viable tissues appear with increased signal intensity allowing the amount of non-viable myocardium to be quantified.
In contrast to separate Cine MR and DEMR acquisitions, Cine-DEMR decreases scanning time by replacing two acquisitions with one thereby supplanting the mental integration of the two sequences with a fused simultaneous visualization. In addition, Cine-DEMR avoids the potential mis-registration of the two separate image sequences. Further, with Cine-DEMR, the phase which best describes non-viable tissue is more likely to be imaged than in DEMR because more than one phase is acquired.
FIG. 1 includes a single-phase DEMR image (image (a)) showing non-viable regions with increased signal intensity (denoted by the arrow) and end-diastolic and end-systolic images (images (b and c)) from a mid-ventricular short axis Cine acquisition. In addition, FIG. 1 includes end-diastolic and end-systolic images (images (d and e)) from a 15-phase Cine-DEMR acquisition. As can be observed, unlike DEMR, non-viable tissue is visible in the end-diastolic and end-systolic Cine-DEMR images. Further, when non-viable tissue is not transmural, it is easier to see how healthy tissue moves in Cine-DEMR as compared to Cine because the healthy and non-healthy regions can be distinguished.
Although Cine-DEMR has both decreased spatial and temporal resolution as compared to individual Cine and DEMR sequences, in recent studies in which clinicians analyzed Cine-DEMR, Cine and DEMR images of the same individual have shown a strong correlation in the categorization of tissues. As such, a need exists for a technique that employs Cine-DEMR to analyze tissue in the LV to enable accurate and efficient diagnosis of heart disease.